Abstract:

A cooling apparatus includes a heat pipe base covering a heat source; a
heat sink with a plurality of heat sink fins; a plurality of heat pipes
connecting the heat pipe base and the heat sink; and a
magneto-hydrodynamic (MHD) pump assembly connected to the heat sink. In a
method for cooling a heat source with heat pipes, magneto-hydrodynamic
(MHD) fluid pipes, and a heat sink, the method includes transmitting heat
from evaporating ends of the heat pipes connected to a heat source to
condensing ends of the heat pipes connected to the heat sink; and
circulating MHD fluid inside the MHD fluid pipes embedded in the heat
sink to dissipate heat. In a method for cooling a heat sink connected to
a plurality of heat pipes and containing a plurality of MHD fluid pipes,
the method includes generating a plurality of magnetic fields using an
array of magnets; creating an electric potential from a top surface to a
bottom surface of each MHD fluid pipe using a plurality of metal films;
and inducing electrically-conductive MHD fluid to circulate in the
plurality of MHD fluid pipes by the plurality of magnetic fields and the
electric potential.

Claims:

1.-8. (canceled)

9. A method for cooling a heat source with heat pipes,
magneto-hydrodynamic (MHD) fluid pipes, and a heat sink, the method
comprising:transmitting heat from evaporating ends of the heat pipes
connected to a heat source to condensing ends of the heat pipes connected
to the heat sink; andcirculating MHD fluid inside the MHD fluid pipes
embedded in the heat sink to dissipate heat.

10. The method according to claim 9, further comprising:driving the MHD
fluid inside the MHD fluid pipes using an MHD pump assembly.

11. The method according to claim 10, further comprising:shielding the MHD
pump assembly with a ferromagnetic metal enclosure.

12. The method according to claim 10, further comprising:controlling the
flow of the MHD fluid by adjusting an electric potential applied to
segments of the MHD fluid pipes in the MHD pump assembly.

13. A method for cooling a heat sink connected to a plurality of heat
pipes and containing a plurality of MHD fluid pipes, the method
comprising:generating a plurality of magnetic fields using an array of
magnets;creating an electric potential from a top surface to a bottom
surface of each MHD fluid pipe using a plurality of metal films;
andinducing electrically-conductive MHD fluid to circulate in the
plurality of MHD fluid pipes by the plurality of magnetic fields and the
electric potential.

14. The method according to claim 13, further comprising:at least
partially shielding the plurality of magnetic fields.

15. The method according to claim 13, further comprising:using a fan on
top of the heat sink to accelerate heat dissipation.

16. The method according to claim 13, further comprising:measuring a
temperature at a location of the heat sink; andadjusting a flow rate of
the MHD fluid circulating in the plurality of MHD fluid pipes.

Description:

BACKGROUND

[0001]A computer system 10, as shown in FIG. 1, includes several
components that are collectively used by a user to perform various
functions such as, for example, preparing and generating a document with
a word processor application. With the computer system 10, the user may
input data to a computing portion 12 using peripheral devices such as a
keyboard 14 or a mouse 16. Data may also be provided to the computing
portion 12 using data storage media (e.g., a floppy disk or a CD-ROM (not
shown)). The computing portion 12, using memory and other internal
components, processes both internal data and data provided to the
computing portion 12 by the user to generate data requested by the user.
The generated data may be provided to the user via, for example, a
display device 18 or a printer 20. The computing portion 12 of a computer
system typically includes various components such as, for example, a
power supply, disk drives, and the electrical circuitry required to
perform the necessary and requested operations of the computer system.

[0002]As shown in FIG. 2, the computing portion 12 may contain a plurality
of circuit boards 22, 24, 26, 28 (e.g., printed circuit boards (PCBs) or
printed wiring boards (PWBs)) on which various circuit components are
implemented. For example, a computing portion designed to have enhanced
sound reproducing capabilities may have a circuit board dedicated to
implementing circuitry that specifically operate to process data
associated with the reproduction of sound.

[0004]In operation, an integrated circuit, such as those shown in FIG. 2,
dissipates heat as a result of work performed by the integrated circuit.
Energy that is needed by the integrated circuit for work is not consumed
with 100% efficiency, thereby resulting in excess energy that is
released, among other things, as heat. As integrated circuits become more
dense (i.e., more transistors per unit area) and faster (i.e., higher
operating frequencies), they generate more heat. As excessive heat is
damaging to an integrated circuit both in terms of performance and
component integrity, an important design consideration involves ensuring
that heat dissipated by an integrated circuit is sufficiently drawn away
from the integrated circuit, where the efficiency of drawing away heat
from the integrated circuit is expressed in terms of what is referred to
as the "heat transfer rate."

[0005]"Heat sinks" are devices that are commonly used to cool integrated
circuits. FIG. 3 shows a heat sink 50 as used with an integrated circuit
52 housed in a package 54 atop a substrate 56. The heat sink 50 is made
of a high thermal conductivity metal (e.g., copper or aluminum). A "high
thermal conductivity metal" is one that allows heat to pass through it
because it contains many free electrons.

[0006]A base of the heat sink 50 is secured over the integrated circuit 52
by, for example, a retention clip (not shown) or an adhesive or thermal
interface material (shown, but not labeled). During operation of the
integrated circuit 52, the temperature of the integrated circuit 52
increases due to increased particle movement resulting from a build-up of
excess energy. The increased integrated circuit temperature results in an
increase in the temperature of the package 54, and consequently, of the
heat sink 50. The increased temperature of the heat sink 50 results in an
increase in the temperature of the air around the heat sink 50, whereby
the heated air rises and effectively draws heat away from the integrated
circuit 52. This process is referred to as "convection."

[0007]The removal of heat dissipated from an integrated circuit by a heat
sink is dependent on numerous factors. For example, the thermal
resistance of the package that houses the integrated circuit affects how
much heat transfers from the integrated circuit to the heat sink. Also,
the effectiveness of the adhesives between the integrated circuit and its
package and the package and the heat sink affects how much heat transfers
between these components. Moreover, the conductivity of the materials
used in the package and the heat sink has a direct bearing on the amount
of heat that is transferred away from the integrated circuit. The surface
area of the heat sink is also important as more surface area results in
more air being heated, thereby resulting in more heat being drawn away
from the integrated circuit by the rising heated air. Efficient cooling
approaches are critical to the performance and reliability of an IC
device with significant power consumption.

SUMMARY

[0008]According to one aspect of one or more embodiments of the present
invention, a cooling apparatus of an IC package comprises: integrated
circuits with one or more heat sources, a heat pipe base covering the
surface of one or more heat sources, a plurality of heat pipes connecting
the heat pipe base and a heat pipe condenser, a heat sink with heat sink
fins connected to the heat pipe condenser, and a magnet array pump
assembly with magneto-hydrodynamic (MHD) fluid pipes inside the heat
sink.

[0009]According to another aspect of one or more embodiments of the
present invention, a method of cooling a plurality of integrated circuits
comprises: attaching a heat pipe base to a heat source, wherein a surface
of the heat pipe base completely covers a surface of the heat source;
connecting a plurality of heat pipes containing fluid to the heat pipe
base; evaporating the fluid from first ends of the plurality of heat
pipes connected to the heat pipe base; condensing the fluid at second
ends of the plurality of heat pipes connected to a heat sink; and cooling
the heat sink by circulating MHD fluid inside MHD pipes embedded in the
heat sink.

[0010]Other aspects and advantages of the invention will be apparent from
the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[0011]FIG. 1 shows a computer system.

[0012]FIG. 2 shows a portion of a computer system.

[0013]FIG. 3 shows a heat sink as used with an integrated circuit.

[0014]FIG. 4A shows a portion of a heat sink in accordance with an
embodiment of the present invention.

[0015]FIG. 4B shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention.

[0016]FIG. 5 shows a cooling apparatus in accordance with an embodiment of
the present invention.

[0017]FIG. 6A shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention.

[0018]FIG. 6B shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention.

[0019]FIG. 6C shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention.

[0020]FIG. 6D shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention.

[0021]FIG. 7 shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention.

[0022]FIG. 8 shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention.

[0023]FIG. 9 shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention.

[0024]FIG. 10 shows a heat sink that may be used in accordance with an
embodiment of the present invention.

[0025]FIG. 11 shows a flow process in accordance with an embodiment of the
present invention.

[0026]FIG. 12 shows a heat pipe with an evaporator on one end and a
condenser on the other end in accordance with an embodiment of the
present invention.

[0027]FIG. 13 shows a heat sink with a plurality of heat pipes which are
placed on top of a microprocessor in accordance with an embodiment of a
prior art.

[0028]FIG. 14 shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention, comprising a PCB, a substrate, a
heat source, a heat pipe base, a plurality of heat pipes with evaporators
and condensers.

[0029]FIG. 15 shows an instance of a cooling apparatus in accordance with
an embodiment of the present invention, comprising a heat source, a
plurality of heat pipes with condensers and evaporators, a heat sink, a
plurality of heat sink fins, and an MHD pump assembly.

[0030]FIG. 16 shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention, comprising a plurality of heat
pipes, a plurality of heat sink fins, a heat sink, a plurality of MHD
fluid pipes, and a MHD pump assembly.

[0031]FIG. 17 shows an MHD pump assembly and MHD fluid pipes which are
embedded in a heat sink in accordance with an embodiment of the present
invention.

[0032]FIG. 18 shows a portion of an array of MHD fluid pipes with copper
films, electrically non conductive materials between and on top of each
pipe, and a ferromagnetic metal shielding cover.

[0033]FIG. 19 shows a lateral view of a portion of a plurality of MHD
fluid pipes, each sandwiched by electrically non-conductive segments and
small pieces of copper film in accordance with an embodiment of the
present invention.

[0034]FIG. 20 shows a portion of a plurality of MHD fluid pipes in
accordance with an embodiment of the present invention, with magnetic
fields and an electrical current direction drawn on the figure.

DETAILED DESCRIPTION

[0035]As described above with reference to FIG. 3, a typical heat sink is
arranged to cool a singly integrated circuit. However, on a circuit board
(e.g., circuit board 22 shown in FIG. 2), there are typically multiple
integrated circuits. While an individual heat sink could be used for
every integrated circuit that is desired to be cooled, in one or more
embodiments of the present invention, a cooling apparatus uses a multiple
magnet array to control fluid flow for cooling multiple integrated
circuits. The multiple magnet array controls fluid flow dependent on
magnetic fields generated in the multiple magnet array. Such cooling is
referred to herein as "magneto-hydrodynamic" cooling.

[0036]Specific embodiments of the invention will now be described in
detail with reference to the accompanying figures. Like elements in the
various figures are denoted by like reference numerals for consistency.
Further, in the following detailed description of embodiments of the
present invention, numerous specific details are set forth in order to
provide a more thorough understanding of the invention. In other
instances, well-known features have not been described in detail to avoid
obscuring the description of embodiments of the present invention.

[0037]FIGS. 4A and 4B show portions of a cooling apparatus in accordance
with one or more embodiments of the present invention. In FIG. 4A, a
multiple magnet array 60 is operatively connected to several groups (or
"levels") of magneto-hydrodynamic pipes 62. The multiple magnet array 60
is arranged to control the flow of fluid in the magneto-hydrodynamic
pipes 62 between a heat spreader (or "heat exchanger") (e.g., a copper
body having a plurality of fins to dissipate heat) (not shown) and one or
more heat sources (e.g., integrated circuits).

[0038]Further, as shown in FIGS. 4A and 4B, groups of the
magneto-hydrodynamic pipes 62 may be operatively connected to an
individual heat sink 64 that is attached to a heat source desired to be
cooled. The individual heat sink 64 may be arranged to at least
temporarily pool fluid delivered for cooling an attached heat source.
Accordingly, those skilled in the art will note that the individual heat
sink 64 may have a cavity for pooling fluid. In such a manner, differing
volumes of fluid may be delivered to the individual heat sink 64 for
cooling of the attached heat source.

[0039]FIG. 5 shows an example of a cooling apparatus in accordance with an
embodiment of the present invention. Particularly, FIG. 5 shows a cooling
apparatus as it is implemented on a circuit board 70. The multiple magnet
array 60 is operatively connected to the magneto-hydrodynamic pipes 62.
The multiple magnet array 60 is also operatively connected to or attached
to a heat sink cooling fins 72. The heat sink cooling fins 72 is arranged
to dissipate heat as air is passed through the heat sink cooling fins 72
(an example of a direction of air flow through the heat sink cooling fins
72 is indicated by the corresponding arrows shown in FIG. 5).

[0040]Fluid carried by the magneto-hydrodynamic pipes 62 may be directed
to one or more integrated circuits (shown, but not labeled) disposed on
the circuit board 70. Further, certain groups of the magneto-hydrodynamic
pipes 62 are arranged to carry heated fluid away from one or more
integrated circuits (shown, but not labeled) disposed on the circuit
board 70.

[0041]FIG. 6A shows a portion of a cooling apparatus in accordance with an
embodiment of the present invention. Particularly, FIG. 6A shows an
example of the multiple magnet array 60. The multiple magnet array 60, as
described above, is arranged to generate a plurality of magnetic fields.
Accordingly, the multiple magnet array 60 may be housed in a
ferromagnetic metal piece 80 arranged to at least partially shield the
plurality of magnetic fields. Those skilled in the art will note that
such shielding may eliminate or at least reduce magnetic interference
with other components (e.g., integrated circuits).

[0042]FIGS. 6B, 6C, and 6D shows interior portions of the multiple magnet
array 60. Within the ferromagnetic metal piece 80, each of the
magneto-hydrodynamic pipes 62 has an electrically non-conductive segment
82. For example, in one or more embodiments of the present invention, a
segment of a magneto-hydrodynamic pipe 62 within the confines of the
ferromagnetic metal piece 80 may be formed of plastic.

[0043]Now, as most clearly shown in FIG. 6D, a first electrical conductor
(shown, but not labeled) is disposed along a portion of each of the
electrically non-conductive segments 82. A second electrical conductor
(shown, but not labeled) is disposed along another portion of each of the
electrically non-conductive segments 82. Connected to each first
electrical conductor (shown, but not labeled) and each second electrical
conductor (shown, but not labeled) are wires 84. The wires 84 may be used
to carry current to or apply voltage to a connected first or second
electrical conductor. In one or more embodiments of the present
invention, the first electrical conductors (shown, but not labeled) and
the second electrical conductors (shown, but not labeled) may be formed
of, for example, copper.

[0044]For purposes of clarity, FIG. 7 shows an example of an individual
magneto-hydrodynamic pipe 62 and electrically non-conductive segment 82
that is housed in a multiple magnet array. In FIG. 7, a first electrical
conductor 86 is attached to a portion of the electrically non-conductive
segment 82. A second electrical conductor (not shown) is attached to
another portion of the electrically non-conductive segment 82.

[0045]Now referring to FIG. 8, the wires 84 connected to each of the first
electrical conductor 86 and the second electrical conductor 88 are used
to create a voltage potential difference between the first electrical
conductor 86 and the second electrical conductor 88. Those skilled in the
art will note that such a voltage potential difference may be created by
causing one of the first electrical conductor 86 and the second
electrical conductor 88 to have a voltage higher than that of the other
of the first electrical conductor 86 and the second electrical conductor
88. As shown in FIG. 8, the second electrical conductor 88 is caused to
have a higher voltage than the first electrical conductor 86, thereby
inducing electrical current flow from the second electrical conductor 88
to the first electrical conductor 86 (direction of induced electrical
current flow indicated by the right-to-left arrows shown in FIG. 8).

[0046]Further, based on an arrangement of magnets within a multiple magnet
array, a magnetic field is also induced across the electrically
non-conductive segment 82 shown in FIG. 8. For example, in FIG. 8, a
magnetic field is induced across the electrically non-conductive segment
82 in a direction indicated by the up-pointing arrows shown in FIG. 8.
Accordingly, a direction of electrically conductive fluid flowing through
the electrically non-conductive segment 82, and consequently, through the
corresponding magneto-hydrodynamic pipe 62, is dependent on a direction
of the induced electrical current and a direction of the magnetic field.
As shown in FIG. 8, the direction of the induced electrical current and
the direction of the magnetic field causes fluid to flow into a plane of
the sheet showing FIG. 8.

[0047]Further, the rate of fluid flow in a magneto-hydrodynamic pipe 62
may be controlled by adjusting a value of the electrical current induced
across the fluid in the corresponding electrically non-conductive segment
82 of the magneto-hydrodynamic pipe 62. Further still, the rate of fluid
flow in a magneto-hydrodynamic pipe 62 may be controlled by adjusting a
strength or orientation of the magnetic field induced across the fluid in
the corresponding electrically non-conductive segment 82 of the
magneto-hydrodynamic pipe 62.

[0048]As described above, a multiple magnet array 60 may be used to direct
fluid to and away from multiple integrated circuits. For each integrated
circuit that may be cooled using the multiple magnet array 60, a set of
magneto-hydrodynamic pipes 62 for carrying fluid toward the integrated
circuit and a set of magneto-hydrodynamic pipes 62 for carrying fluid
away from the integrated circuit are provided. An example of such sets of
magneto-hydrodynamic pipes 62 is shown in FIG. 9.

[0049]The magneto-hydrodynamic pipes 62 operatively connected to the
multiple magnet array 60 are each associated with a heat sink of an
integrated circuit that may be cooled using the multiple magnet array 60.
FIG. 10 shows an example of a heat sink 90 that may be used in accordance
with an embodiment of the present invention. The heat sink 90 has a
plurality of "fins" 92 allowing for and facilitating the dissipation of
heat away from the heat sink 90. A plurality of magneto-hydrodynamic
pipes 62 extend through the heat sink 90. Those skilled in the art will
note that in one or more embodiments of the present invention, the
magneto-hydrodynamic pipes 62 extending through the heat sink 90 may be
integral with a body of the heat sink 90.

[0050]One end of each of the magneto-hydrodynamic pipes 62 is associated
with a temperature sensor 96 embedded in a thermal interface material 98
disposed on a lid 100 positioned over an integrated circuit 102 and
substrate 104. One another end of each of the magneto-hydrodynamic pipes
62 is operatively connected to a multiple magnet array 60 as described
above.

[0051]Each temperature sensor 96 is configured to measure/sense a
temperature at a particular location (or "hot spot) of the integrated
circuit 102. Further, those skilled in the art will note that the sizing
and arrangement of one or more of the temperature sensors 96, the thermal
interface material 98, and the lid 100 may be adjusted so as to improve
the accuracy of temperature measurements taken by one or more of the
temperature sensors 96.

[0052]In one or more embodiments of the present invention, one or more of
fins 92, magneto-hydrodynamic pipes 62, and lid 100 may be formed of a
thermally conductive material. For example, one or more of fins 92,
magneto-hydrodynamic pipes 62, and lid 100 may be formed of copper.

[0053]Further, in one or more embodiments of the present invention, a heat
sink may have a different fin configuration than that shown in FIG. 10.
Moreover, those skilled in the art will note that the heat sink 90 shown
in FIG. 10 is not necessarily to scale and is not limited to a particular
length, width, and/or height.

[0054]Further, although the heat sink 90 in FIG. 10 is shown as having a
certain number of magneto-hydrodynamic pipes 62, in one or more other
embodiments of the present invention, a different number of
magneto-hydrodynamic pipes may be used.

[0055]As described above, a magneto-hydrodynamic pipe in a heat sink used
with or as part of a cooling apparatus in accordance with one or more
embodiments of the present invention has an end that is associated with a
temperature sensor on a lid disposed over an integrated circuit. By using
the temperature readings taken by the temperature sensor, a multiple
magnet array of the cooling apparatus may be adjusted so as to effectuate
a desired response with respect to cooling of a hot sport of a particular
integrated circuit.

[0056]FIG. 11 shows an example of a flow process in accordance with an
embodiment of the present invention. In FIG. 11, a temperature sensor is
used to take a temperature reading at a location of an integrated circuit
ST110. The temperature reading may be transmitted to, for example, a
control module that calculates certain adjustments based on the
temperature reading ST112. The adjustments may be made in reliance on
assuming that ambient air flow conditions, cooling apparatus, and/or heat
sink parameters remain constant. In such a manner, the parameters
associated with a multiple magnet array of the heat sink may be adjusted
without being dependent on varying ambient, heat sink, or cooling
apparatus conditions.

[0057]In ST114, adjustments to the multiple magnet array of the heat sink
are made based on the calculations in ST112. These adjustments may
involve, for example, adjusting an electrical current induced across
fluid in one or more segments in the multiple magnet array. In such a
manner, the rate of fluid flow may be adjusted so as to more quickly or
more slowly dissipate heat away from one or more hot spots.

[0058]Those skilled in the art will note that the control module may be
any device or medium usable to make adjustment calculations. For example,
the control module may be part of another integrated circuit or may be a
software module executable by the integrated circuit being cooled.
Further, in one or more embodiments of the present invention, a separate
integrated circuit dedicated for controlling the parameters of the
multiple magnet arrays may be implemented.

[0059]FIG. 12 shows an example of a heat pipe with an evaporator 121 on
one end of the pipe and a condenser 122 on the opposite end. In one
configuration in accordance with an embodiment of the present invention,
the evaporator 121 is connected to a heat source and the condenser 122 is
connected to a heat sink. A heat pipe typically comprises a vacuum tight
envelope, a wick structure and a working fluid. The atmosphere inside the
heat pipe is set by an equilibrium of liquid and vapor. As heat enters at
the evaporator 121 on one end of the heat pipe, this equilibrium is
broken, generating vapors at a slightly higher pressure. This higher
pressure vapor travels to the condenser 122 located at the other end of
the heat pipe where the slightly lower temperatures cause the vapor to
condense, giving up its latent heat of vaporization.

[0060]Heat pipes remove heat from the source in a two-phase process. A
liquid at one end of the pipe evaporates when exposed to heat and
releases the heat to a heat sink by condensation at the other end. The
condensed fluid is then pumped back to the evaporator by the capillary
forces developed in the wick structure. This continuous cycle can
transfer large quantities of heat with minimal thermal gradients. The
operation of a heat pipe is passive, driven only by the heat transfer and
therefore results in high reliability and durability.

[0061]FIG. 13 shows an example of heat pipes 132 embedded in heat sink
fins 131. A heat spreader 133 is placed on top of a heat source such as a
microprocessor. The weight of a vertical heat sink 130 with embedded heat
pipes can become very heavy and cause reliability problems to the
microprocessor underneath. The assembly and attachment of the vertical
heat sink 130 are difficult and complex in real application.

[0062]FIG. 14 shows a portion of an embodiment of the present invention. A
cooling apparatus 140 on a printed circuit board 144 has a substrate 143,
a heat source such as a microprocessor 145, a heat pipe base 142 which
covers the top surface of the microprocessor 145, a plurality of L-shaped
heat pipes 141, and a heat pipe condenser 146. The evaporator ends of the
heat pipes 141 are connected to the heat pipe base 142 and the opposite
ends of the heat pipes 141 are connected to the heat pipe condenser 146.
Using L-shaped heat pipes reduce the burden of weight placed on the
microprocessor by keeping the heat pipe condenser 146 and the heat sink
with fins at a remote location. The reduction of weight greatly improves
the mechanical reliability of the microprocessor 145.

[0063]FIG. 15 depicts a portion of a cooling apparatus 150 in accordance
with an embodiment of the present invention. A heat source such as a
microprocessor sits on top of a heat-resistant substrate 156. The heat
pipe base 151 completely covers the heat source and transmits heat to a
condenser 152 by vaporization and condensation of liquid contained in the
heat pipes 155. A plurality of heat sink fins 153 attached to the heat
pipes 155 integrate MHD pump assembly 154 and MHD pipes which are
embedded in the heat sink fins. The use of embedded MHD pipes in the heat
sink fins 153 significantly reduces thermal gradient and heat dissipation
from the heat sink.

[0064]FIG. 16 displays another view of a cooling apparatus 160 in
accordance with an embodiment of the present invention. A plurality of
heat pipes 164 transfers heat to a heat sink 163 by condensation. MHD
fluid pipes 161 are embedded in the heat sink fin structure 164 and
enhance the rate of heat dissipation by providing MHD fluid circulation
within the heat sink 163. An MHD pump assembly contains a plurality of
magnets and metal strips to generate magnetic fields and electric
potential to force or "pump" MHD fluid in a particular direction.

[0065]FIG. 17 shows an external view of an MHD cooling apparatus 170,
taken out from the heat sink structure. A number of convoluted MHD fluid
pipes 172 is connected to a ferromagnetic metal enclosure 171 containing
MHD pump assembly. The ferromagnetic metal enclosure 171 prevents the MHD
pump assembly from damaging other devices with magnetic field leakage.
Furthermore, the convolution of pipe is designed to maximize the surface
area of the plurality of pipes inside the heat sink structure for high
thermal transfer. Each layer of pipe circulates MHD fluid and efficiently
cools the heat sink structure.

[0066]FIG. 18 shows an internal view of an MHD pump assembly 180 in
accordance with an embodiment of the present invention. An array of metal
pipes 182 is separated from each other and sandwiched by electrically
non-conductive material 184 such as plastic. Small pieces of metal films
inserted to top and bottom surfaces of the non-conductive material,
contacting the array of metal pipes 182 and creating an electric
potential inside each pipe. In one or more embodiments of the present
invention, both metal pipes and metal films are made of copper.
Furthermore, magnets are placed on top and bottom of the spaces between
metal pipes. A ferromagnetic metal shielding cover 181 encapsulates the
MHD pump assembly to prevent damaging of other devices by magnetic field
leakage.

[0067]FIG. 19 gives a detailed view of a portion of an MHD pump assembly
in accordance with an embodiment of the present invention. Small pieces
of metal film 196 are attached to top and bottom surfaces of an array of
metal pipes and electrically non-conductive segments separate metal pipes
from each other. In one or more embodiments of the present invention, a
positive voltage is applied to the top metal films by an electrical wire
193 and a negative voltage is applied to the bottom metal films by an
electrical wire 192. Non-metal materials 194 create gaps between segments
of magnets 191. In this particular embodiment, the magnets 191 are placed
above and below the spaces between metal pipes.

[0068]FIG. 20 shows a cross-sectional view of an array of metal pipes in
accordance with an embodiment of the present invention. In this
particular embodiment, a top metal film 201A is positively charged and a
bottom metal film 201B is negatively charged, creating an electric field
203 pointing downward. Magnets placed below the spaces between metal
pipes create a counterclockwise magnetic field in pipe 204, a clockwise
magnetic field in pipe 205, and a counterclockwise magnetic field in pipe
206. One skilled in the art can use the Right-Hand Rule of physics to
determine the direction of force applied to MHD fluid. In the pipes 204
and 206, the downward direction of electric charge 203 and
counterclockwise magnetic fields 202A and 202C create forces into the
page. In the pipe 205, the clockwise direction of magnetic field 202B and
the downward direction of electric charge 203 create a force out of the
page. These electromagnetically induced forces will act as an MHD pump in
one or more embodiments of the present invention.

[0069]Advantages of the present invention may include one or more of the
following. In one or more embodiments of the present invention, a cooling
apparatus may be used to cool one or more integrated circuits disposed on
a circuit board.

[0070]In one or more embodiments of the present invention, a flow of
thermally conductive fluid used to cool one or more hot spots of an
integrated circuit may be controlled so as to effectuate a desired level
of cooling.

[0071]In one or more embodiments of the present invention, a multiple
magnet array for driving the flow of fluid used to cool one or more hot
spots of an integrated circuit resides separate from the integrated
circuit.

[0072]In one or more embodiments of the present invention, a multiple
magnet array may be used to have multiple channels cool across an area of
an integrated circuit, where the multiple magnet array may also be used
to more directly cool a hot spot of an integrated circuit.

[0073]In one or more embodiments of the present invention, a magnetic
field used to drive the flow of fluid used to cool one or more hot spots
of an integrated circuit may be shielded so as to prevent magnetic field
interference.

[0074]In one or more embodiments of the present invention, a plurality of
heat pipes with evaporators on one end and condensers on the other end
may be used to dissipate heat from one or more heat sources, wherein the
condensers are connected to one or more heat sinks containing MHD fluid
pipes.

[0075]In one or more embodiments of the present invention, a heat sink may
be connected to a heat source by a plurality of heat pipes, wherein the
heat sink does not sit on top of the heat source, hence reducing
unnecessary weight placed on the heat source.

[0076]In one or more embodiments of the present invention, an MHD fluid
pumping assembly with MHD pipes embedded in a heat sink may be used to
decrease temperature gradient across heat sink fins.

[0077]In one or more embodiments of the present invention, a cooling
apparatus comprising a plurality of heat pipes connecting one or more
heat sources to a heat sink containing MHD fluid pipes provides highly
efficient cooling by using both passive (heat pipes) and active (MHD
fluid pipes) thermal transfer.

[0078]While specific embodiments of the present invention have been shown
and described, further modifications and improvements will occur to those
skilled in the art. It is understood that the invention is not limited to
the particular forms shown and it is intended for the appended claims to
cover all modifications which do not depart from the spirit and scope of
this invention.